1. Field of the Invention
The present invention is generally related to cable television (CATV) radio frequency tuners and, in particular, to a low-cost, high-integration, high-performance, compact CATV compatible RF tuner/transceiver.
2. Description of the Related Art
The design of radio frequency transmitters and receivers, or transceivers, has been and remains problematic due to the related problems of RF radiation sensitivity of the circuit and circuit components and the propensity for active components to radiate in-band and in harmonically related RF bands. Consequently, the shielding and layout of RF circuits, such as those used in the CATV frequency band of 5 to 860 MHz, remains a primary design consideration for RF circuits.
The use of RF circuits, particularly those targeted to operate within the CATV range of frequencies (generally 5 to 860 MegaHertz), has become quite common as the CATV cable plant in particular has been implemented over wider geographic areas. The cable head-end systems, operated by local or regional Cable Operators as the source of cable content programming, are typically sophisticated, high-performance, and correspondingly expensive RF transmitter systems. The physical size, power consumption, and operating maintenance requirements of these head-end systems have been and generally remain secondary considerations in the design and construction of the head-end systems. This prioritization in the features and functions of head-end systems is a conventionally accepted consequence of the fact that a single head-end system is capable of serving large numbers of tail-end or client systems. In addition, with increasing ratios of tail to head-end systems, the power and performance requirements on the head-end system increase at much greater than linear rates, if only due to the larger geographic area involved and the larger amount of noise injection due to greater numbers of connections to tail-end systems.
Conversely, conventional receiver-only, or tuner, tail-end systems are largely driven by low-cost due to the commoditization of such systems. The size, power requirements, and RF shielding of the packaged tail-end systems are all easily within acceptable ranges without much if any exceptional design considerations. Particularly with regard to the RF shielding, other than compartmental shielding for the highest-frequency portion of the circuit, often little more than a simple ferritic coating on the insides of the system housing is used. Since the enclosed circuitry is conventionally a singular RF receiver/tuner, the sensitivity of the circuitry in general to RF radiation is much less than conventionally required in full RF transceiver applications, including in particular those employing digital RF transceivers.
Conventionally, nothing more than a receiver-only tail-end system was required or previously even usable. However, with the expansive growth of wide-area networks, such as the Internet, a need has been recognized to provide a tail-end system transmitter function. Specifically, the target of so-called cable-modem Internet Service Providers (ISPs) is to use the existing CATV cable plant as a high-performance, likely asymmetric, bidirectional data network. Current cable modem systems are able to broadcast network data to tail-end systems. Return network data, however, is presently transported through the existing analog telecommunications network. The requirement for a separate analog modem and the cost of making the return data connections are well recognized as undesirable and an impediment to the wide adoption of cable modem technologies.
Present efforts to package a transmitter in tail-end systems range from loosely packaging a separate transmitter within the overall tail-end system housing to providing a separate transmitter and receiver on a common printed circuit board separated by complex shielding conventionally recognized as necessary to preserve the independent function of the transmitter and receiver sections. In all cases, the design complexity, manufacturing tolerance design limitations, post-manufacture circuit tuning requirements, and resultant cost is generally viewed as inappropriate for commoditization of transceiver tail-end cable modem systems, particularly for mass-consumer oriented customer premises equipment (CPE).
Consequently, there is a clear need for a new tail-end system design that achieves full functional support for a CATV RF frequency transceiver that is suitable for commoditization.